Rubber goods and method of manufacturing the same



Patented Mar. 20, 1934 iii STATES UNi RUBBER GOODS AND METHOD OF MANU- FACTURENG THE SAPJE Edward Arthur Murphy,

and Douglas Frank Twiss, Coldfield, England, assigncrs Erdington, Birmingham, Wylde Green, Sutton to Dunlop Rubber Company Limited, a British corporation No Drawing. Application Serial No. 517,299. In 1930 21 Claims.

This invention comprises improvements in or relating to the manufacture of goods of rubber or similar material and is particularly concerned with the production of homogeneous compositions of rubber or similar material from aqueous dispersions thereof of the kinds hereinafter specified, the present application being a continuation-in-part of our co-pending application Serial No. 406,154, filed November 9, 1929.

An object of the invention is to effect by the addi ion of one or more of certain hereinafter specified compounding ingredients under hereinafter defined conditions the coagulation of the aqueous dispersions of rubber or similar material into crumb-like or powder-like compositions which when dried have the following particularly useful properties.

Another object of the present invention is to produce homogeneous, crumb-like or powderlike compositions of rubber or similar material from aqueous dispersions thereof ofithe kinds hereinafter specified and further to produce such compositions in admixture with, disintegrated organic materials, e. g. ground rubbered cotton waste, ground tyre carcasses, ground vulcanized rubber waste, cotton or other fibres, disintegrated cork, wood flour, wood pulp, husk meal, disintegrated rawhide, leather dust, disintegrated gutta-percha or asphaltum. I f

It is found, for example, that the application of pressure to these crumb-like or powder-like compositions effects their consolidation and that for mixtures of normal type, c. g. for motor treads, etc., the mere operation of warming between rollers in the normal manner can impart the necessary consistency of plasticity for direct calendaring profiling and extruding.

It is also found that where these crumb-like or powder-like compositions contain very high proportions of compounding ingredients these compositions may be employed in the manner of mother stocks and can be incorporated with rubber on a mill'in known manner or may themselves be directly consolidated to form leather-like compositions. The consolidated compositions may be made to contain homogeneously. dispersed throughout their mass higher proportions of compounding ingredients such as gas black than can be introduced by compounding rubber in known manner on the mill.

According to the invention the crumb-like or powder-like character is obtained by first adding to the aqueous dispersions of rubber or similar material certain hereinafter specified substances which are commonly used as compounding in- February 20, 1931, Great Britain March 31,

(Cl. MiG-23) gredients, but which when added in the usual manner in sufficient amounts to latex, cause coagulation; their coagulative effect is, however, arrested at this stage by the presence of suitable stabilizing substances until the thorough mixing 60 of the latex and compounding ingredients has been effected.

The protective influence of the stabilizing agents is then lowered by the addition of the hereinafter specified compounding ingredients 5 referred to for the effecting of the agglomeration. 1 These substances are added in sufiicient quantity to induce agglomeration or incipient coagulation, but insufficient to lead to the formation of a coherent coagulum.

The invention comprises stirring the aqueous ispersions hereinafter specified during the operation, of compounding in the presence of a protective colloid or protective colloids of the types herein mentioned, and performing the com- 75 pounding operation under such conditions that whereas, the ratioof the protective colloids to the compounding ingredients throughout the initial stages of compounding does not allow any substantial coagulation to take place, a critical s0 ratio is subsequently attained such that coagulation is made to occur in the form of crumb-like or powder-like compositions.

Examples of compounding ingredients suitable for introduction. into the aqueous dispersions in 5 the first stage of the process are gas black, clay, various grades of amorphous silica, whiting.

Examples of compounding ingredients which induce the agglomeration at the second stage are gas black, amorphous silica and basic oxides such 9 as zinc oxide, lime and magnesia.

If a composition containing fibrous fillers is desired, the compounded dispersions of rubber or the like thus obtained may be then admixed with disintegrated organic filling materials, preferably '95 properly wetted as for instance with an aqueous solution of ammonium oleate. Thereafter the mixtures produced in this manner are coagulated by the addition, while stirring, of the compounding ingredients hereinbefore mentioned as belonging to the second stage of the process.

The compounding ingredients to be added in the first stage of the process are first dispersed in water with the aid of predetermined, suitably 105 adjusted quantities of protective colloids and when these aqueous dispersions of compounding ingredients are added to the aqueous dispersions of rubber or similar material the protective colloids prevent in known manner the coagulano hereinbefore compounding ingredients tion of these dispersions of rubber or material.

The compounded dispersions thus obtained may be thereafter made to wet comparatively coarse particles of disintegrated organic materials su h as ground rubber waste, cotton fibre, wood flour, leather dust or disintegrated guttapercha. .By comparatively coarse particles are meant particles which have for their greatest linear dimensions a size ranging for instance from 0.1 m. to 5 m. m. These admixtures are then converted in a second stage into crumb-like compositions by the addition of, for example, zinc oxide or lime and are subsequently dried. When coagulation is afterwards effected by the addition while stirring of the compounding ingredients specified as belonging to the second stage, the formation of the usual type of continuous coherent mass d es not occur; a discontinuous agglomer tion of flocculent or of loose crumb-like charac er is obtained instead.

This stage of the process may be effected in two ways. The protective influence of the stabilizing agents used in admixing the compounding ingredients added in the first stage of the prccess'may be lowered by the addition of substances, viz, those classed in the second stage of the process which are themselves compounding ingredients, but which because of their particular way of dispersion, had they been added to the aqueous dispersions of rubber or the like material which had not been treated with the compounding ingredients specified as belonging to the first stage of the process, would not effect coagulation. It is only because these compounding ingredients classed in the second stage of the process are added to an already compounded latex, compounded in the manner hereinbefore described that the agglomeration is effected probably due to the instability produced by their influence on the protective colloids already present.

In certain cases, however, the addition of one or more of the compounding ingredients classed in the second stage of the process may bring about agglomeration due to having effected a prior experimental adjustment in the ratio of to protective colloids so that the final ratio of compounding ingredients to the protective colloids, although sufficient to disperse the compounding ingredients properly is insufficient to prevent the particular type of coagulation desired in the compounded latex.

This second manner of carrying the invention into eifec is particularly applicable where the compounding ingredients used to effect the agglomeration are of the same nature-as those added to the aqueous dispersion of rubber or the like material in thefirst place.

The protective colloids used may be of such a nature as to lead to a softening efiect on the dry compounded rubber thereby, if desired, permitting it subsequently to be extruded or calenda red without previous mastication or substantial mastication. Also by suitable choicev of rotective colloids employed, no detrimental effect is observed in the mechanical properties of the vulcanized rubber. The agglomeration of the aqueous dispersion of rubber or the like material into the form of crumb or powder allows the similar compounded rubber produced at this stage to be washed, if desired, for the removal of soluble substances therefrom and to be easily dried and to be subsequently easily manipulated in manufacturing processes, e. g. in molding operations. The undried material may be shaped, for instance, by

spreading, pressure, moulding. The dried mass can be plasticized on an ordinary mixing mill, profiled or extruded, moulded and vulcanized.

The advantages obtained according to the present invention are that mixings can be produced in which the particles of disintegrated organic materials are present in a matrix consisting of a comparatively small quantity, for instance, about 20 per cent on the total mixture of high quality reinforced mixing which acts as a strong binding agent for them in the finished product.

Mixings can also be produced containing large proportions of disintegrated organic materials for instance about 7o per cent on the total mixing such as cotton fibre, ground vulcanize rubber waste, Wood flour, leather dust, which are suitable for moulding, profiling and extruding operaions which could not be obtained by compounding in the normal manner. 7

The dispersions comprise by way of example, those consisting of or containing rubber, guttapercha, balata or similar vegetable resins occurring naturally or artificially obtained and in vulcanized or unvulcanized condition. Aqueous dispersions of coagulated rubber, synthetic rubber, vulcanized rubber, waste or reclaim, may also be employed, if desired, as alternatives or admix tures. These materials are hereinafter designated as rubber material.

Any of the aforesaid dispersions may contain the usual known compounding ingredients and/or may be in concentrated form.

it has been found that ammonium compounds of organic acids such as ammonium oleate, ammonium stearate and ammonium resinate, are examples of protective colloids whi h fulfill the necessary requirements. They are good dispersing agents. They allow the formation of discontinuous crumb-lilac under the described conditions. They decompose on drying, leaving the corresponding organic acids in the crumb. These acids can exert suificient softening eifect on the rubber to enable extrusion without previous substantial mastication, whilst during subsequent vulcanization the combination of the resulting cids with the zinc oxide present provides any substantial softening eifect by these acids in the vulcanized rubber.

Compounds of the higher fatty acids with the alkali metals can also be used in place of the corresponding ammonium compounds; in this case, however, the alkali metal naturally remains there or may be removedby washing with water.

Concentrates such as are obtained in Patent 1,846,164, Feb. 28, 1932, in which may be incorporated any one or more of the usual compounding ingredents may also be used.

The following are given by way of example as to how the process can be effectedl. A latex mixing having the following composition- Parts by weight Rubber 61 Sulphur 3. 5 Zinc oxide 5. 0 Gas black; 27. 0 Oleic acid 3. 5

added slowly to sufficient latexconcentrated to give the desired 61 parts of rubber and the mixture is stirred mechanically for a'few'mi-nutes, for example, by means of a rotating wire mesh paddle or by agitation in a mechanicalmixing hopper such as is commonly used in the preparation of rubber solutions or doughs. The five parts of zinc oxide, previously dispersed-in 10 parts of water containing 0.05 part of caseinand 0.05 part of glue, are then added and the stirring continued. After a fewminutes considerable thickening takes place leading to the formation of a viscous mass which soon changes into a fine crumb. The crumb can either be washed with water or placed immediately on racks to dry, or may be passed through rollers or pi aced in presses to squeeze out the bulk of the water. The dry mass when heated, for example, by short treatment on warming mills, is ready for extrusion, calendaring or other treatment.

It should be noted that in this example although agglomeration and subsequent crumb formation do not take place until after thezinc oxide dispersion has been added, mechanical agitation of the type indicated of such a dispersion with latex in the absence of gas black does not cause coagulation or even thickening of the latex. It is assumed that the protective action of the am monium oleate is reduced so that it becomes just insuflicient to protect the latex from the coagulating effect of the gas black. If the proportion of the oleic acid given in the example is decreased to any appreciable extent, e. g., to 2.5 parts, thickening and ultimate flocculation tend to occur in an uncontrollable manner even with- Parts by weight Rubber; 20.0 Sulphur 1. 0 Gas black 30.0

Zinc oxide 4.0 Oleic acid 1.0

Rosin 3.0

is made up in the following -manner parts of gas black and 1 part of sulphur are mixed with parts ofwater containing an ammoniacal solution of 3 parts of rosin and 1 part of oleic acid. The mixture is mechanically stirred for a short time and then added to sufficient latex concentrated to give 20 parts of rubber. After a few minutes stirring, 4 parts of zinc oxide dispersed as in the first example, are added and the stirring continued.

The mass soon changes to a fine crumb which when dry, yields a powdery substance capable of being passed through a 60 mesh sieve.

This material when passedthrough warm mixing mills immediately consolidates into a coherent sheet and, with or without vulcanization, yields a tough leather-like product.

Alternatively, by mixing this material in suitable proportion with rubber on a mixing mill it may be used as a rapid and convenient means of compounding gas black in the preparation of reinforced rubber mixings.

It is found that the homogeneous rubber compositions obtained according to this invention are suitable during the crumb-like or powderystage for the manufacturae. g., by molding, of a large variety of articles such as tiles and boot soles, while after the crumb-like or powder compositions have-been consolidated by pressure, the material can be used for the manufacture of sheet for flooring, pram tyring and treads for tyres.

A cheap mix which can be rendered plastic on a mixing mill having the following compositionis prepared in the following manner:

The gas black is dispersed together with the sulphur in an aqueous solution of the bulk of the oleic acid as ammonium oleate and the dispersion thus obtained is' mixed with sufficient latex to give the desired proportion of rubber.

The ground rubber cotton Waste and mineral rubber are first disintegrated to agranular condition and are thenmixed with sufficient water ammoniacal solution to ensure their being properly wetted. This mixture is then addedto the latex-gas black dispersion. After sufficient gentle agitation has been givento the mixture to ob tain uniform distribution of the latex-gas black dispersion throughout the mass, it is coagulated by the addition of zinc oxide previously made into a paste with water. In the crumb-like compositions so formed the particles of the disintegrated organic materials are surrounded or coated by rubber gaseblack sulphur compositions.

. The crumb-like compositions obtained may be shaped as such or may be dried and moulded or plasticized on a mixing mill when they are ready for profiling, extruding'or moulding.

' What we claim is:

1. A process for themanufacture of homogeneous crumb-like or'powder-like compositions of rubber material'from aqueous dispersions thereof,

which'comprises introducing into said aqueous dispersion a water insoluble compounding ingredient without lessening the protective colloids suffieiently to cause coagulation, admixing the aforesaid compounded dispersion with disintegrated organic material and thereafter stirring i. A process as claimed in claim 1 wherein the compounding ingredient added in the first stage of the process is dispersed in water with the aid of predetermined, suitably adjusted quantities of protective colloids.

5. A process as claimed in claim 1 wherein the 1 containing the remainder of the oleic acid in disintegrated organic materials are used as comparatively coarse particles, having for their greatest linear dimensions, a size ranging from about 0.1 mm. to 5 mm.

6. A process as claimed in claim 1 wherein zinc oxide is used in the coagulating stage to convert the admixtures intocrumb-like compositions.

'7. A process as claimed in claim 1 wherein the disintegrated organic materials are present in large proportions as for instance about '70 per cent on the total mixing.

8. A process as claimed in claim 1 wherein the disintegrated organic materials are bound together by a comparatively small quantity of high quality reinforced mixing as for instance about per cent on the total mixture.

9. A process as claimed in claim 1 wherein the disintegrated organic materials are disintegrated waste rubber materials.

10. A process as claimed in claim 1 wherein the compounding ingredients added in the first stage of the process are dispersed in water with the aid of ammonium oleate as a protective colloid.

11. A process as claimed in claim 1 wherein a basic compounding ingredient is used in the coagulating stage to convert the admixtures into crumb-like compositions.

12. A process of manufacturing homogeneous crumb-like compositions which comprise mixing rubber latex with an aqueous dispersion of sulphur and gas black with an oleate as a protective colloid, mixinga wetted disintegrated rubbered cotton waste and mineral rubber with said mix ture, said waste and mineral rubber being wetted with an oleate, said mixture being stirred while said waste materials and mineral rubber are added, and adding a paste of zinc oxide and water to said mixture in quantity just sufiicient to render said dispersion unstable.

13. A process of making crumb-like rubber compositions from an aqueous rubber dispersion which comprises mixing with the dispersion a water insoluble filling material dispersed in a dispersing medium with protective colloids to form a stable uniform mixed dispersion with said latex and adding to said mixed dispersion relatlvely smaller quantities of additional ,water 'insoluble compounding filling material without sufficient protective colloids for a stable dispersion Water insoluble filling ingredients dispersed in a dispersion medium while maintaining in said dispersion medium sufiicient protective colloids to prevent coagulation and adding additional water insoluble filling ingredients to said mixed dispersion while decreasing the proportion of protective colloids below that required to maintain the resulting mixture as a stable dispersion and terminatingsaid decrease in the proportion of protective colloids immediately upon passing below the critical limit required for a stable dispersion whereby the solids will agglomerate or precipitate into crumb-likematerial.

15. A process of making crumb-like rubber compositions from latex which comprises mixing with latex water insoluble filling ingredients dispersed in a dispersion medium while maintaining in said dispersion medium sufiicient protective colloids to prevent coagulation and adding additional water insoluble filling ingredients to said mixed dispersions while decreasing the proportion of protective colloids to such an extent as to permit the agglomeration, but not sufficiently to lead to the formation of a coherent coagulate whereby the solids will agglomerate or precipitate into crumb-like material.

16. The process of claim 13 in which the water insoluble ingredients added during the decreasing of the proportion of protective colloids are of the same nature as those previously added.

17. The process of claim 13 in which the protective colloid has a softening eiiect on the dried compounded rubber material.

18. The process of claim 13 in which the protective colloid is an ammonium salt of an organic fatty acid.

19. The process of claim 13 in which the protective colloid is ammonium oleate.

20. The process of claim 13 in which the protective colloid is an alkali salt of a higher fatty acid.

21. A process of forming crumb-like rubber compositions from latex which comprises dispersing about 27 parts of gas black and 3 parts of sulphur in parts of water containing 3 parts of oleate acid as ammonium oleate, adding the resulting dispersion to a concentrated latex comprising approximately 60% of rubber, mixing said dispersions and adding to said mixed dispersions 5 /2 parts of casein and 5 parts of glue and 5 parts of zinc oxide dispersed in 10 parts of Water whereby the solids will agglomerate or precipitate into crumb-like material.

EDWARD ARTHUR MURPHY.

DOUGLAS FRANK TWISS. 

